Atherosclerosis is the pathology underlying several of mankind's most lethal diseases, such as myocardial infarction and peripheral arterial occlusive disease (PAOD). PAOD represents atherosclerosis of the large and medium arteries of the limbs, particularly to the lower extremities, and includes the aorta and iliac arteries. It often coexists with coronary artery disease and cerebrovascular disease. Persons with PAOD are at increased risk of other vascular events such as myocardial infarction or stroke [Waters, R E, Terjung R L, Peters K G & Annex B H. J. Appl. Physiol. 2004; Ouriel K. Lancet, 2001, 258:1257-64; Kroger, K. Angiology, 2004, 55:135-138]. Clinically significant lesions may gradually narrow the peripheral arteries leading to pain on walking usually relieved by rest (claudication), ischemic ulcers, gangrene, and sometimes limb amputation. Medical therapy is generally ineffective but operations bypassing or replacing the lesion with artificial or venous grafts improve blood flow distally, at least until they become restenosed [Haustein, K. O., Int. J. Clin. Pharmacol. Ther., 35:266 (1997)]. Recently, it has been discovered through human genetic linkage studies that DNA variants of the PTGER3 gene that encodes the prostaglandin E2 receptor subtype 3 (known as EP3) increase the risk of an individual developing PAOD (see US published application 2003/0157599). Thus, antagonists of prostaglandin E2 (PGE2) binding to the EP3 receptor may provide effective treatment or prophylaxis for PAOD.
In response to various extracellular stimuli, prostaglandins are rapidly generated from free arachidonic acid through the consecutive action of the cyclo-oxygenases and synthases. The prostaglandins exert their action in close proximity to the site of their synthesis. To date, eight prostanoid receptors have been cloned and characterized. These receptors are members of the growing class of G-protein-coupled receptors. PGE2 binds preferentially to the EP1, EP2, EP3, and EP4 receptors; PGD2 to the DP and FP receptors; PGF2α, to the FP and EP3 receptors; PGI2 to the IP receptor and TXA2 to the TP receptor. PGE2 binding to the EP3 receptor has been found to play a key role in the regulation of ion transport, smooth muscle contraction of the GI tract, acid secretion, uterine contraction during fertilization and implantation, fever generation and hyperalgesia. The EP3 receptor has been detected in many organs such as the kidney, the gastrointestinal tract, the uterus and the brain. In the cardiovascular system, EP3 is expressed by vascular endothelium and smooth muscle, and at least four isoforms of EP3 are expressed on human platelets [Paul, B. Z., B. Ashby, and S. B. Sheth, Distribution of prostaglandin IP and EP receptor subtypes and isoforms in platelets and human umbilical artery smooth muscle cells. British Journal of Haematology, 1998. 102(5): p. 1204-11.]
Prostanoids, acting through specific membrane receptors belonging to the superfamily of G protein-coupled receptors (GPCRs) have an essential role in vascular homeostasis, including platelet function regulation. Among the prostanoids, thomboxane A2 (TxA2) is a potent stimulator of platelet aggregation, whereas prostaglandin (PG) I2 inhibits their activation. On the other hand, prostaglandin E2 (PGE2) has been reported to have a biphasic effect on platelet response, potentiating their aggregation at low concentrations and inhibiting it at higher concentrations. It has been shown that the stimulatory effects of PGE2 on platelet aggregation are exerted mainly through EP3 receptor, one of the four subtypes of receptors activated by PGE2.
Local synthesis of prostaglandins in the arterial vessel wall may play a profound role in atherosclerosis. While only COX-1 is present in the healthy vessel wall, both COX-1 and COX-2 are present in arteriosclerotic plaque [Schonbeck, U., et al., Augmented expression of cyclooxygenase-2 in human atherosclerotic lesions. Am J Pathol, 1999. 155(4): p. 1281-91; Cipollone, F., et al., Overexpression of functionally coupled cyclooxygenase-2 and prostaglandin E synthase in symptomatic atherosclerotic plaques as a basis of PGE2-dependent plaque instability. Circulation, 2001. 104(8): p. 921-7]. Their increased expression, together with increased expression of prostaglandin E synthase, may account for the increased production of PGE2 noted above. In genetically modified mice lacking the low density lipoprotein receptor (LDL-R), formation of atherosclerotic plaque can be reduced by treatment with rofecoxib, a selective inhibitor of COX-2, through reducing production of PGE2 and other prostaglandins [Burleigh M E, Babaev V R, Oates J A, Harris R C, Gautam S, Riendeau D, Marnett L J, Morrow J D, Fazio S, Linton M F. Cyclooxygenase-2 promotes early atherosclerotic lesion formation in LDL receptor-deficient mice. Circulation. Apr. 16, 2002;105(15):1816-23].
Within the atherosclerotic plaque, vascular smooth muscle cells have been shown to express EP3 receptors and PGE2 stimulates their proliferation and migration, a hallmark of atherosclerotic plaque formation [Blindt R, Bosserhoff A K, vom Dahl J, Hanrath P, Schror K, Hohlfeld T, Meyer-Kirchrath J. Activation of IP and EP(3) receptors alters cAMP-dependent cell migration. Eur J Pharmacol. May 24, 2002;444(1-2):31-7]. It is, therefore, plausible that chronically inflamed vessels produce sufficient quantities of PGE2 to activate EP3 receptors on vascular smooth muscles cells (contributing to atherosclerotic lesion formation) and on platelets (contributing to thrombosis). Locally produced PGE2 (from platelets themselves, vessel wall components, and inflammatory cells) potentiates platelet aggregation by suboptimal amounts of prothrombotic tissue factors, which might not cause aggregation by themselves, through priming of protein kinase C. The intracellular events triggered by activation of the EP3 receptor may enhance platelet aggregation by opposing the effect of PGI2 and enhancing the effects of primary aggregating agents such as collagen. EP3 receptor activation may therefore contribute to atherosclerosis and the risk of thrombosis observed in pathological states such as vasculitis and PAOD.
Current treatments for PAOD either address increased risk for cardiovascular events such as myocardial infarction and stroke, or provide symptomatic relief for claudication. All of these treatments affect platelet function. Treatments reducing risk for cardiovascular events include low dose asprin (sufficient to reduce platelet aggregation while still permitting the production of PGI2 by the vessel wall) and inhibitors of the platelet adenosine diphosphate receptor inhibitor (clopidogrel). Binding of adenosine diphosphate to the platelet adenosine diphosphate receptor causes a drop in platelet cAMP with consequent platelet activation and aggregation. Treatments providing symptomatic relief from claudication include platelet phosphodiesterase type 3 inhibitors such as cilostazol which act to increase intracellular levels of cAMP. Inhibitors of the platelet adenosine diphosphate receptor or the platelet phosphodiesterase type 3 act directly or indirectly to increase the content of cAMP in platelets, thereby inhibiting platelet activation and consequent aggregation with thrombus formation. PGE2 binding to EP3 acts to decrease cAMP, therefore an antagonist of PGE2 binding to the EP3 receptor, by opposing the PGE2-dependent decrease in cAMP needed to induce platelet activation and consequent aggregation, or by opposing the PGE2-dependent decrease in vascular smooth muscle cell cAMP needed to stimulate migration, might be expected to provide therapeutic benefit in PAOD. Such an antagonist may also be disease-modifying by inhibiting or reducing atherosclerotic plaque formation.
Prostaglandins furthermore have been implicated in a range of disease states including pain, fever or inflammation associated with rheumatic fever, influenza or other viral infections, common cold, low back and neck pain, skeletal pain, post-partum pain, dysmenorrhea, headache, migraine, toothache, sprains and strains, myositis, neuralgia, synovitis, arthritis, including rheumatoid arthritis, degenerative joint diseases (osteoarthritis), gout and ankylosing spondylitis, bursitis, burns including radiation and corrosive chemical injuries, sunburns, pain following surgical and dental procedures, immune and autoimmune diseases; cellular neoplastic transformations or metastic tumor growth; diabetic retinopathy, tumor angiogenesis; prostanoid-induced smooth muscle contraction associated with dysmenorrhea, premature labor, asthma or eosinophil related disorders; Alzheimer's disease; glaucoma; bone loss; osteoporosis; Paget's disease; peptic ulcers, gastritis, regional enteritis, ulcerative colitis, diverticulitis or other gastrointestinal lesions; GI bleeding; coagulation disorders selected from hypoprothrombinemia, hemophilia and other bleeding problems; and kidney disease.
While circulating levels of prostanoids are extremely low in healthy individuals [FitzGerald G A, Brash A R, Falardeau P & Oates J A. JCI 1981 68:12472-1275], the local concentration of PGE2 can dramatically increase in inflammatory states. For example, the local production of PGE2 was shown in vitro to increase more than 30-fold in aortoiliac occlusive disease [Reilly J, Miralles M, Wester W & Sicard G. Surgery, 1999, 126:624-628]. It is, therefore, plausible that chronically inflamed vessels produce sufficient quantities of PGE2 to activate EP3 receptors on platelets. In this environment, the intracellular events triggered by activation of the EP3 receptor may enhance platelet aggregation by opposing the effect of PGI2 and enhancing the effects of primary aggregating agents such as ADP. EP3 receptor activation may therefore contribute to the thrombosis observed in pathological states such as vasculitis and atherosclerosis. Peripheral Arterial Occlusive Disease (PAOD) is an atherosclerotic illness that affects primarily the elderly as a consequence of occlusion of the lumen of peripheral arteries, mainly the femoral artery and it is associated with an increased risk of vascular events as myocardial infraction or stroke [Waters, R E, Terjung R L, Peters K G & Annex B H. J. Appl. Physiol. 2004; Ouriel K. Lancet, 2001, 258:1257-64; Kroger, K. Angiology, 2004, 55:135-138]. Several clinical studies have shown that treatment with prostaglandins improves PAOD symptoms [Reiter M, Bucek R, Stumpflen A & Minar E. Cochrane Database Syst. Rev. 2004, 1:CD000986; Bandiera G, Forletta M, Di Paola F M, Cirielli C. Int. Angiol. 2003, 22:58-63; Matsui K, Ikeda U, Murakami Y, Yoshioka T, Shimada K. Am. Heart J. 2003, 145:330-333] supporting the linkage between PAOD and prostanoid receptor function.
Ortho-substituted phenyl acylsulfonamides and their utility for treating prostaglandin-mediated disorders are described in U.S. Pat. No. 6,242,493 and in two articles by Juteau et al. [BioOrg. Med. Chem. 9, 1977-1984 (2001)] and Gallant et al. [BioOrg. Med. Chem. Let. 12, 2583-2586 (2002)], the disclosures of which are incorporated herein by reference.